1. Field of the Invention
The present invention generally relates to an optical fiber. In particular, the present invention relates to an optical-fiber drawing system for drawing an optical fiber from an optical fiber pre-form.
2. Description of the Related Art
In a typical optical-fiber drawing process, an optical fiber pre-form is softened to its melting point and then pulled or drawn into a thin bare optical fiber. This bare optical fiber (also referred to as “bare glass”) is hot enough to be sensitive to external contaminants before it is coated. Therefore, the bare optical fiber must be protected from contaminants such as atmospheric dust. To this end, gas or air is blown towards the bare optical fiber. Further, the bare optical fiber is cooled by passing it through a cooling apparatus. The cooled bare optical fiber is then coated.
FIG. 1 illustrates a side view of an optical-fiber drawing system according to the conventional art. In FIG. 1, a furnace 120, a cooler 140, a coating applicator 150, an ultra-violet (UV) curer 170 and a capstan 180 are shown.
The furnace 120 is hot enough to maintain a temperature of at least 2,000° C. thus softening the end of an optical pre-form in order to generate a bare optical fiber 130 from the softened pre-form.
The cooler 140 cools the optical fiber to a temperature suitable for coating the bare optical fiber 130 and includes a cooling tube for cooling gas, i.e., helium, through which to flow. Further, a coolant such as cooling water, liquid nitrogen, or the like is circulated through a spacing between the inner and outer walls of the cooling tube so as to insulate the cooler 140.
The coating applicator 150 is provided with a path filled with atmospheric gas, through which the bare optical fiber passes. The coating applicator 150 has a retainer in which liquid coating material fed from its storage tank (not shown) is contained. The bare optical fiber is coated in the course of passing through the retainer. The coating material, like various types of UV curable resin, is curable under UV radiation. Alternatively, a thermosetting resin may be used as the coating material.
The UV curer 170 cures the coating material coated on a circumference of the bare optical fiber, i.e., the UV curable resin under UV radiation.
The capstan 180 pulls the cured bare optical fiber 160 under a predetermined force so that the cured bare optical fiber can be drawn continuously at a constant diameter.
The optical fiber 160 has a very small diameter of 125±0.2 μm. Consequently, when the drawn optical fiber has a non-uniform profile resulting from accidental scratching, a microstructure defect of the optical fiber pre-form, unstable coating pressure, etc., during drawing at a high speed, a scattering phenomenon may be created in the optical fiber. If this scattering phenomenon becomes large enough for detection during a megascopic check, most operators may be able to cope with it. In fact, it is difficult to observe a minute scattering phenomenon without the aid of any tool, which acts as a factor of quality failures. In addition, as this scattering phenomenon is dependent on an observing angle, it is difficult to measure precisely.